pub fn dp_rec_mc(amount: u32) -> u32 {
    // 币种含：1、2、5、10、20、30、50、100元
    let mut amount = amount;
    let _100 = amount / 100;
    amount = amount - _100 * 100;
    let _50 = amount / 50;
    amount = amount - _50 * 50;
    let _30 = amount / 30;
    amount = amount - _30 * 30;
    let _20 = amount / 20;
    amount = amount - _20 * 20;
    let _10 = amount / 10;
    amount = amount - _10 * 10;
    let _5 = amount / 5;
    amount = amount - _5 * 5;
    let _2 = amount / 2;
    amount = amount - _2 * 2;
    _100 + _50 + _30 + _20 + _10 + _5 + _2 + amount
}
